In a cellular communication system, a terminal receives a sync signal from a neighbor cell through cell discovery, secures a time and frequency sync of the neighbor cell, and obtains a number (i.e., a physical cell ID) of the neighbor cell, and as necessary, primary cell common control information. A base station simultaneously sends sync signals and cell common control information to all of the terminals in the cell using an antenna transmitting or receiving signals in all directions in the cell. Further, the terminal, because using an omni-directional antenna, simultaneously receives signals from neighboring base stations as well as the serving base station and does not experience interference with communication with the serving cell.
However, the terminal should measure the receive power of the neighbor cell to determine additional handover from the serving cell to the neighbor cell, but at the moment of measuring the receive power of the neighbor cell, the terminal might not decode signals from the serving cell depending on implementations of the terminal. Thus, the terminal sends a request for a gap time to the serving base station to measure the receive power of the neighbor cell, and during the gap time, the terminal may stop communication with the serving cell and measure the receive power of a reference signal from the neighbor cell. Further, the terminal uses the gap time to detect a base station and cell using a frequency different from the frequency that the serving cell uses.
However, in case the terminal uses the gap time, the communication efficiency is deteriorated due to the process of requesting the serving cell to allocate the gap time and receiving a response to discovery the neighbor cell. In particular, in case all of the terminals in the cell make use of the gap time allocation method whenever attempting to discovery a cell, the communication efficiency may drastically worsen.
As another example, when all of base stations send sync signals and cell common control information during the same, fixed slot time in a beamforming cellular communication system where a base station and a terminal transmit and receive signals through beamforming, the beamforming terminal sequentially switches receive beams while receiving signals from the serving cell and signals from a neighbor cell to sync with the serving cell and to discovery the neighbor cell in order to receive signals whatever directions the base station of the serving cell and the base station of the neighbor cell are positioned in. In such conventional beamforming cellular communication systems, in case the slot time allocated for sync signal and cell common control information does not have a fixed length, the terminal may fail to receive some signals from the serving cell or discover the neighbor cell due to the cell discovery operation. Further, since, in the conventional beamforming cellular communication systems, base stations use different beamforming apparatuses and methods per cell, a problem arises even when the length of a slot time allocated for sync signal and cell common control information differs from cell to cell. In particular, in case a slot time for sync signal allocated in the neighbor cell is longer than that in the serving cell, the terminal may receive none of sync signals from the neighbor cell and may resultantly fail to discover the neighbor cell. In case all of the base stations perform a cell discovery operation in compliance with the maximum slot length for sync and cell common control information allocable to address all such issues, the discovery of the neighbor cell may succeed, but a failure to receive control signals or data from the serving cell may occur, causing a failure in communication with the serving cell.
Thus, there is required a scheme for performing cell discovery by efficiently allocating a cell discovery time for cell discovery per terminal in a beamforming cellular communication system.